1. Field of the Invention
The present invention relates to an electrical parking brake device, and more specifically, relates to an electrical parking brake device including a parking brake that is applied and released by electrical drive.
2. Description of the Related Art
An electrical parking brake device, typically, is constituted by an operation switch and a control circuit or an Electronic Control Unit (ECU). The operation switch keeps the state of whether to apply a parking brake, based on the operation by a driver. The control circuit checks the state of the operation switch, and based on this, issues an application command, a release command or the like for the brake of a vehicle. The operation switch and the control circuit, typically, are connected by a plurality of signal wires. Such an electrical parking brake device has a deep relation with the safety of the vehicle, and therefore, a secure application control based on fail-safe and the like is required even when a failure occurs in the operation switch. In addition, the number of components mounted in the interior of the vehicle has increased because of the recent demand for vehicle performance advance and the like. Therefore, it is required that the structure of the operation switch and the control circuit is a simple and space-saving structure.
As described in Japanese Translation of PCT International Application Publication No. 2010-512277, there is a conventional electrical parking brake device in which a malfunction diagnosis unit, a power source line and a ground line are provided in the operation switch in addition to switches, and five conductors are provided between the operation switch and the control circuit. Further, as described in Japanese Patent Laid-Open No. 2014-104880, there is proposed another conventional electrical parking brake device in which a switch control circuit (SWECU) is provided between the operation switch and the control circuit, and the switch control circuit and the control circuit are connected by a CAN communication line. Furthermore, as described in U.S. Pat. No. 8,432,060, another conventional electrical parking brake device actualizes a compact structure in which outside wires to be connected with the operation switch are only four conductors between the operation switch and the control circuit, but the operation switch is constituted by switches and diodes.
Here, in the electrical parking brake device in Japanese Translation of PCT International Application Publication No. 2010-512277, the internal structure of the operation switch is complicated, and in addition, the operation switch, which is connected with a power source line, a ground line and five signal wires, is complicated. Further, in the electrical parking brake device in Japanese Patent Laid-Open No. 2014-104880, the operation switch and the control circuit are connected by only a CAN communication line, allowing for simplification. However, the operation switch is provided with the switch control circuit, and in the switch control circuit, it is necessary to perform CAN communication interface processing, in addition to the check of the state of whether to apply the parking brake, resulting in complication. Furthermore, in the electrical parking brake device in U.S. Pat. No. 8,432,060, current direction limiting elements such as diodes are added in the operation switch.